Methods for indication of at least one subsurface barrier characteristic and methods of use

ABSTRACT

A containment system for use adjacent to a selected region of a subterranean formation and comprising a plurality of laterally interlocked casing strings. At least one electrically conductive element is disposed along at least a portion of a casing string and is used for performing electrical time domain reflectometry. At least one protective element may be positioned between portions of adjacent casing strings of the barrier, and at least one electrically conductive element may be disposed at least partially within the at least one protective element for use in indicating at least one characteristic of at least a portion of the containment system. Electrical time domain reflectometry (TDR) may be used to indicate the at least one characteristic; for instance, TDR may be used to indicate leakage through the barrier or a discontinuity or void in a barrier filler material.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/850,636filed May 20, 2004 entitled APPARATUS FOR INDICATION OF AT LEAST ONESUBSURFACE BARRIER CHARACTERISTIC now U.S. Pat. No. 7,056,063, which isa continuation-in-part of U.S. application Ser. No. 10/358,633, filedFeb. 4, 2003, now U.S. Pat. No. 6,910,829, issued Jun. 28, 2005 andentitled IN SITU RETRIEVAL OF CONTAMINANTS OR OTHER SUBSTANCES USING ABARRIER SYSTEM AND LEACHING SOLUTIONS AND COMPONENTS, PROCESSES ANDMETHODS RELATING THERETO, which is a continuation-in-part of U.S.application Ser. No. 10/062,817, filed Feb. 1, 2002, now U.S. Pat. No.6,758,634 issued Jul. 6, 2004 and entitled SUBSURFACE MATERIALSMANAGEMENT AND CONTAINMENT SYSTEM, COMPONENTS THEREOF AND METHODSRELATING THERETO, which claims the benefit of U.S. ProvisionalApplication No. 60/267,320, filed Feb. 6, 2001 entitled SUBSURFACEMATERIALS MANAGEMENT AND CONTAINMENT SYSTEM, the disclosure of each ofwhich is incorporated by reference herein in its entirety, respectively.

GOVERNMENT RIGHTS

The United States Government has rights in the following inventionpursuant to Contract No. DE-AC07-99ID13727 and Contract No.DE-AC07-05ID14517 between the U.S. Department of Energy and BattelleEnergy Alliance, LLC.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods, apparatus andsystems for measuring at least one characteristic of a subsurfacebarrier. Particularly, the methods, apparatus, and systems of thepresent invention relate to measuring at least one characteristic of aninterlocking structure formed between adjacent adjoined casing sectionsthat form, at least partially, a barrier for waste containment.

2. State of the Art

Containment, management, and disposal of various types of waste, such aschemical, nuclear, and other potentially harmful types of waste arerecognized, longstanding problems. It is also well recognized thatburied waste may often include heavy metals such as mercury or cadmium,carcinogenic materials such as trichloroethylene, radioactive materials,or other hazardous substances. Further, hazardous materials withinburied waste may be leached (i.e., carried from within a liquid)therefrom, into surrounding soil and into the groundwater. Because wateris used for human consumption and for agriculture, contamination ofgroundwater by leaching is a major concern.

However, the contamination caused by buried waste may not be limitedsolely to groundwater. For instance, contaminated groundwater may becarried into other waterways such as streams, rivers, and lakes, thuspolluting those waterways and leading to poisoning of plant and animallife. In addition, polluted waterways pose a threat to humans as well,particularly in the case of waterways and bodies of water used forrecreational purposes or as sources of drinking or irrigation water.

Also, while many of the problems associated with buried waste concernthe effect of leachate on water systems, buried waste may also emit gasphase contaminants that may cause deleterious effects if not containedand managed. For instance, such gas phase contaminants may pollute thesoil and the groundwater, and may build up to unsafe pressures whichcould ultimately result in explosion or pollution of the atmosphere byventing of the gas.

Accordingly, a variety of methods and devices have been devised toattempt to resolve the problems related to buried waste. These remediesmay be broadly grouped into the categories of remediation andcontainment. Generally, remediation focuses on processes designed tochange the chemical composition of a contaminated material orcontaminant to a more benign chemical composition, while containmentremedies seek to isolate contaminants and contaminated material withinan area or remove them from an area.

Remediation approaches such as biological treatments, thermal processes,and chemical processes may be problematic for a variety of reasons. Inparticular, many remediation techniques may be expensive and potentiallyhazardous. Further, it may be difficult to verify the effectiveness ofmany remediation treatments. Also, determining the proper or optimumremediation technique for a given contamination scenario may be, initself, a complex and time-consuming process.

Containment, barrier, or in situ approaches are problematic as well. Oneknown containment approach is simply to dig up and remove thecontaminated soil for treatment or disposal. This approach is expensiveand time-consuming and often accomplishes little more than moving theproblem to another location. Of course, finding an acceptable ultimatedisposal location is another significant impediment to movement of acontaminated region. Other containment approaches may involve installingvertical barriers, horizontal barriers, or both types of barriers aroundthe buried waste. In theory, this approach is attractive because it doesnot require digging up or otherwise disturbing the buried waste.

However, conventional containment or barrier systems suffer from avariety of inadequacies including a lack of durability, corrosionresistance, and structural integrity. These inadequacies are a functionof numerous factors associated with the environment in which thecontainment or barrier systems are located including, but not limitedto: exposure to harsh chemicals such as concentrated saline solutions,saturated calcite and gypsum solutions; exposure to extreme thermalgradients; and exposure to stresses induced by shifting in the earth. Inaddition, conventional barrier systems may suffer from inadequateability to monitor or verify the integrity thereof as well as inadequatereparability thereof if a failure should occur.

Accordingly, recently, containment systems that are designed to contain,collect, or process effluent which would otherwise escape from a zonecontaining waste materials, have been developed. One such containmentsystem is disclosed in U.S. Pat. No. 6,575,663 to Kostelnik, et al.,assigned to the assignee of the present invention, the disclosure ofwhich is incorporated in its entirety by reference herein. Moreparticularly, U.S. Pat. No. 6,575,663 discloses a barrier comprising aseries of adjacent casing strings that are interlocked with one anotherand may be filled with a barrier filling material to form asubstantially continuous wall.

Also, U.S. Pat. No. 5,800,096 to Barrow discloses a subsurface barrierhaving a number of interconnected columns. In addition, U.S. Pat. No.5,800,096 to Barrow discloses that the interconnected region between twointerconnected columns may be filled with wax, grout, polymer, or otherviscous sealer via pipes disposed proximate to the interconnected regionand having outlets directed toward the interconnected region.

While the above-mentioned exemplary containment systems may form arelatively stable and corrosion resistant containment system, it may bedesirable to monitor the effectiveness or integrity of the containmentsystem after formation or during formation thereof. For instance, it maybe desirable to determine the presence of deficiencies in the materialsused to form a barrier. Similarly, it may be desirable to detect leaksthrough the barrier which may carry contaminated materials thereacross.

For instance, U.S. Pat. No. 6,575,663 also discloses a “smart casing”that may include joint integrity sensors comprising acoustic/ultrasonictime domain reflectometry sensors that detect cracks and large voids instructures such as smart casing sections or optical fiber sensors whichmay indicate strain measurements in smart casing sections and mayindicate the presence of voids and cracks therein.

U.S. Pat. Nos. 6,016,714 and 6,648,552 to Smith, each of which areassigned to the assignee of the present invention and each of thedisclosures of which is incorporated in its entirety by referenceherein, each discloses placement of conductors for detecting any strain,i.e., a change in dimension, which takes place in the material of abarrier. Specifically, strain will generally elongate the conductorswhere the strain occurs and this will result in a change in thecharacteristic impedance of the affected conductors. U.S. Pat. Nos.6,016,714 and 6,648,552 to Smith disclose that such a change incharacteristic impedance can be measured with electrical time domainreflectometry; thus, indication of strain and the location of suchstrain may be identified and data might advantageously be collected viaa computer-based data acquisition system.

In view of the conventional apparatus, methods, and systems formonitoring or verifying the integrity of waste containment structures,it may be desirable to provide improved methods, apparatus, and systemsfor monitoring the integrity of a waste containment structure,particularly a substantially continuous barrier formed of adjacentcasing strings.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a containment system for containingmaterial within a selected region of a subterranean formation.Particularly, the present invention relates to a barrier for wastecontainment. For instance, a barrier of the present invention mayinclude a plurality of casing strings, wherein each of the plurality ofcasing strings is adjoined to at least another laterally adjacent casingstring of the plurality of casing strings by way of an interlockingstructure. Further, the plurality of casing strings may be sized,positioned, and configured to collectively form a continuous barrierabout, or at least adjacent, a selected region. In addition, at leastone electrically conductive element may be disposed along at least aportion of the length of at least one of the casing strings, the atleast one electrically conductive element configured to communicate anelectrical signal for performing electrical time domain reflectometry.

Such a configuration may be desirable for determining at least onecharacteristic of the barrier or an adjacent region of the subterraneanformation in which it is disposed. For instance, the at least oneelectrically conductive element may be positioned within theinterlocking structure of each of the plurality of casing strings.Alternatively, where each of the plurality of casing strings includes abore, the at least one electrically conductive element may be positionedwithin a bore of one or more of the plurality of casing strings.

In another aspect of the present invention, the containment system mayinclude at least one protective element which is sized, positioned, andconfigured for protecting at least one electrically conductive elementdisposed at least partially therein. Alternatively or additionally, theprotective element may be sized, configured, and positioned for sealingbetween portions of adjacent casing strings. Also, at least oneprotective element may be sized and positioned for maintaining a desiredspacing between portions of adjacent casing strings. In an exemplaryembodiment, the containment system may comprise two protective elements,and each of the two protective elements may include at least oneelectrically conductive element.

In a further aspect of the present invention, a containment system maycomprise at least two electrically conductive elements which aredisposed along a predicted leakage path. Such a configuration may bedesirable for detecting leaks through the barrier.

The present invention also relates to a method of indicating at leastone characteristic of at least a portion of a containment system forcontaining material within a selected region of a subterraneanformation. Particularly, a plurality of casing strings may be provided,wherein each of the plurality of casing strings is adjoined to at leastanother adjacent casing string of the plurality of casing strings by wayof an interlocking structure. Further, the plurality of casing stringsmay be positioned to collectively form a continuous barrier adjacent theselected region. In addition, at least one electrically conductiveelement may be disposed along at least a portion of the length of atleast one of the plurality of casing strings forming the barrier and atleast one characteristic associated with the barrier or a region of thesubterranean formation adjacent thereto may be indicated responsive toperforming electrical time domain reflectometry via the at least oneelectrically conductive element.

As mentioned above, the at least one electrically conductive element maybe disposed within the interlocking structure of at least one of theplurality of casing strings. Also, the at least one electricallyconductive element may be disposed at least partially within aprotective element.

Indicating at least one characteristic of the barrier or adjacent regionmay include detecting a change in the impedance responsive to performingelectrical time domain reflectometry via the at least one conductiveelement, indicating a location of the change in impedance responsive toperforming electrical time domain reflectometry via the at least oneelectrically conductive element, or both.

In addition, electrical time domain reflectometry may be performed viathe at least one electrically conductive element more than once,selectively, at random, on a periodic basis, substantially continuously(e.g., at least 10,000 times per second), or a combination thereof,without limitation.

In another aspect of the present invention, at least one interlockingstructure between two adjacent casing strings of the plurality of casingstrings of the barrier may be substantially filled with barrier fillermaterial. The present invention contemplates that an electrical timedomain reflectometry process may be performed during or aftersubstantially filling the at least one interlocking structure withbarrier filler material. Alternatively, an initial electrical timedomain reflectometry process may be performed before the filling processand at least a subsequent electrical time domain reflectometry processmay be performed spaced in time, during or after the filling process. Ofcourse, results of the initial and the at least a subsequent electricaltime domain reflectometry processes may be compared.

Indication of leakage through the barrier or a discontinuity or void inbarrier filler material within the barrier may be identified in responseto performing one or more electrical time domain reflectometryprocesses.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention can be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIG. 1A shows a perspective cut-away view of a barrier of the presentinvention;

FIG. 1B shows a cross-sectional view of two interlocked, adjacent casingsections of a portion of the barrier shown in FIG. 1A;

FIG. 1C shows an enlarged partial cross-sectional view of theinterlocking structure shown in FIG. 1B;

FIG. 1D shows a graphical representation of a TDR technique;

FIG. 1E shows a schematic enlarged partial cross-sectional view of theinterlocking structure shown in relation to buried waste;

FIG. 1F shows an enlarged partial cross-sectional view of aninterlocking structure of the present invention including a protectiveelement;

FIG. 1G shows an enlarged partial cross-sectional view of an alternativeembodiment of an interlocking structure including a protective elementof the present invention;

FIG. 1H shows an enlarged partial cross-sectional view of anotheralternative embodiment of an interlocking structure including aprotective element of the present invention;

FIG. 2A shows a cross-sectional view of an alternative embodiment of twointerlocked, adjacent casing sections of a barrier;

FIG. 2B shows a cross-sectional view of another embodiment of twointerlocked, adjacent casing sections of a barrier;

FIG. 3A shows an enlarged partial cross-sectional view of aninterlocking structure of the present invention;

FIG. 3B shows a simplified schematic longitudinal cross-sectional viewof the interlocking structure shown in FIG. 3A;

FIG. 3C shows an enlarged partial cross-sectional view of aninterlocking structure of the present invention;

FIG. 3D shows a simplified schematic longitudinal cross-sectional viewof the interlocking structure shown in FIG. 3B;

FIG. 4 shows an enlarged partial cross-sectional view of an interlockingstructure as shown in FIG. 1B;

FIG. 5A shows a partial cross-sectional view of two adjacent casingstrings which form a portion of a barrier according to the presentinvention disposed within a formation; and

FIG. 5B shows an enlarged partial cross-sectional view of aninterlocking structure of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows a perspective cut-away view of a barrier 140 which may beformed by the methods of the present invention. As shown in FIG. 1A, apipe jacking apparatus 111 and microtunneling machine 102 may beemployed to form a plurality of adjacent casing-lined tunnels underneatha subsurface region 110. Particularly, casing strings 142 may comprise aplurality of casing sections 120 affixed to one another and extendinglongitudinally (lengthwise) in an end-to-end relationship and may bedisposed within subterranean formation 108, as by tunneling or drillingmethods and apparatus as known in the art. Further, the casing strings142 disposed within the adjacent tunnels may be interlocked to form asubsurface barrier 140.

Preferably, each tunnel may be substantially circular in cross-sectionand may begin in trench or pit 112 extending to a corresponding trench(not shown) on the other side of subsurface region 110. Casing sections120 may typically comprise steel. However, alternative materials thatwould provide desirable mechanical and material properties anddurability are contemplated as being within the scope of this invention.

Further, as adjacent tunnels may be formed and lined with casingsections 120, a side wall of each casing section 120 of casing string142 installed within a tunnel may be interlocked, during tunneling ordrilling into formation 108, with a side wall of an adjacent casingsection 120 of a casing string 142 disposed within an adjacent tunnel sothat a continuous barrier 140 may be formed. Accordingly, each of casingsections 120 of one casing string 142 may be laterally adjoined to orinterlocked with casing sections 120 of an adjacent casing string 142 bycomplementary interlocking structures (not shown). For instance, casingsections 120 may comprise interlocking structures as described in U.S.patent application Ser. No. 10/062,817 to Nickelson or U.S. patentapplication Ser. No. 10/358,633 to Nickelson, each of which applicationsis assigned to the assignee of the present invention and the disclosureof each of which is incorporated in its entirety by reference herein.

More specifically, FIG. 1B shows a partial cross-sectional view of aportion of barrier 140 including two interlocked, adjacent casingsections 120, each casing section 120 including a substantially circularbody 126 forming a bore 127. Alternatively, each of casing sections 120may comprise other tubular cross-sectional shapes, as known in the art.In addition, each of casing sections 120 may include at least one maleinterlocking structure 124 and at least one female interlockingstructure 122. Each female interlocking structure 122 may include achannel feature 123, which forms, in combination with portions of itsassociated substantially circular body 126, a recess 121. Optionally, afrangible closure element 144 may be disposed to close the mouth 137formed between the circumferentially adjacent portions of substantiallycircular body 126 associated with a recess 121. Of course, disposing amale interlocking structure 124 within a female interlocking structure122 may perforate the frangible closure element 144 associated therewithas the leading end of the male interlocking structure 124 proceedslongitudinally within the female interlocking structure 122 of anadjacent casing string 142 (FIG. 1A), according to the drilling ortunneling process for forming casing-lined tunnels mentioned above.

In the embodiment shown in FIG. 1B, interlocking structure 230 mayinclude a male interlocking structure 124, which is configured as agenerally L-shaped outwardly extending feature, relative to thesubstantially circular body 126 of casing section 120, which may bedisposed within an associated female interlocking structure 122. It maybe noted that the at least one female interlocking structure 122including recess 121 may be disposed within the bore 127 of a casingsection 120 and the frangible closure element 144 may be provided on theouter radial surface of its substantially circular body 126 as shown inFIG. 1B.

As known in the art, casing sections 120 of casing strings 142 (FIG. 1A)as well as interlocking structures 230 of adjacent casing sections 120,may be preferably substantially filled (within their bores 127, recesses121, or both) with a barrier filler material (not shown) such as grout,wax, tar, cement, concrete, bentonite-based materials, modified cement,polysiloxane, acrylic polymers, or the like. For instance, barrierfiller material may comprise wax which is flowed within casing strings142 (FIG. 1A) and interlocking structures 230 thereof and subsequentlysolidifies to form a substantially leak-tight barrier 140 (FIG. 1A).More generally, barrier filler material comprising a liquid, slurry,granular material, or other flowable state (i.e., freely movable) may bedisposed within the interlocking structures 230 and, optionally, may besubsequently solidified to form a substantially continuous leak-tightbarrier 140. Also, as known in the art, barrier filler material disposedwithin bores 127, recesses 121, or both of casing sections 120 mayproduce a barrier 140 that is relatively chemically stable, even whenexposed to solutions saturated with calcite, gypsum, or other reactivesolutions.

Such a barrier configuration may be desirable, because a barrier 140including interlocked casing strings 142 (FIG. 1A) as well as includingbarrier filler material (not shown) may exhibit a high degree ofstructural continuity and strength. Additionally, such a barrier 140 maydemonstrate a relatively low hydraulic conductivity, which means thatbarrier 140 may be substantially impermeable to leachate or gas emittedfrom buried waste 133 (FIG. 1A). Barrier 140 may also be thermallystable and may retain its structural integrity and hydraulicconductivity under a wide variety of physical and thermal conditionsincluding ground shifting, and relatively large temperature gradients.Also, barrier 140 may be configured for use in environments thatexperience cyclical freeze and thaw temperature conditions and inenvironments where precipitation may cause the presence of groundwaterflow.

Therefore, it may be desirable to both verify the integrity of thebarrier 140 upon or during its initial formation and to further verifythe subsequent condition of the barrier 140 or, more particularly, theinterlocking structures 230 thereof, after its initial formation. Forinstance, it may be desirable to measure or indicate that the barrierfiller material has substantially uniformly filled voids within aninterlocking structure 230 extending between adjacent, adjoined casingstrings 142. It may also be desirable to determine or evaluate thepresence of liquid within or proximate barrier filler material generallywithin an interlocking structure 230, because such presence may indicateat least the possibility of a leak or path through the barrier 140.While the materials and structural members comprising a casing string142 may be generally selected to exhibit an initial suitable durability,monitoring performance over time of a barrier 140 may be of particularinterest. Further, monitoring the integrity (impermeability) of aninterlocking structure 230 may be of particular interest because ifadjacent interlocked casing sections 120 move relative to one another,the barrier filler material (not shown) within interlocking structure230 may suffer damage prior to either the male interlocking structure124 or the female interlocking structure 122 of the adjacent casingsections 120, respectively. More generally, monitoring the integrity(impermeability) of an interlocking structure 230 or barrier 140 may bedesirable due to the long-term exposure thereof to chemicals, water, orforces.

FIG. 1C shows an enlarged partial cross-sectional view of aninterlocking structure 230 as shown in FIG. 1B. Particularly,interlocking structure 230 may comprise protective elements 220 that maybe disposed between a portion of the male interlocking structure 124extending into recess 121 of a female interlocking structure 122 and thelongitudinal edges of circular body 126 bounding the mouth 137 of recess121. Protective elements 220 may be generally configured for protectingone or more electrically conductive element 240 disposed at leastpartially therein, respectively.

Additionally or alternatively, protective elements 220 may be configuredfor effecting a seal between casing sections 120. For instance,protective elements 220 may be resilient and may be disposed betweenmale interlocking structure 124 and the edges of substantially circularbody 126 of bounding the mouth 137 of recess 121 of a laterally adjacentcasing section 120 into which male interlocking structure 124 extends.Such an arrangement, wherein protective elements 220 are compressedbetween a portion of male interlocking structure 124 and the edges ofcircular body 126 bounding the mouth 137 of recess 121, maysubstantially close the recess 121 to form a chamber. Forming a chambercomprising recess 121 may be desirable for both containing barrierfiller material (not shown) therein and for preventing a leaktherethrough. It may also be appreciated that protective elements may besized and positioned for maintaining a desired spacing between portionsof adjacent casing sections 120.

Protective elements 220 may each incorporate one or more electricallyconductive elements 240 that may extend therein along the length of acasing string 142. Electrically conductive elements 240 may eachcomprise an electrically conductive wire which is completelyencapsulated within a respective protective element 220. Alternatively,an electrically conductive element 240 may be exposed at a surface ofits associated protective element 220, without limitation. Accordingly,an electrically conductive element 240 may be at least partiallyencapsulated within a protective element 220, according to the presentinvention. Each of electrically conductive elements 240 may comprise acoaxial cable or another electrical conductor which is electricallycapable of carrying an electrical signal suitable for performingelectrical time domain reflectometry.

Such a configuration may be desirable for indicating a characteristic ofthe barrier 140 proximate to the protective element 220 or within anyregion encompassed by the electrical influence of an electricallyconductive element 240, by way of electrical time domain reflectometry(TDR). TDR may include introducing a voltage signal or waveform (usuallyconfigured with a relatively fast rise time, such as a step function)into the electrically conductive element and then observing the waveformas it is reflected by the transmission system (i.e., the electricallyconductive element and its surrounding electrical environment). When theinput signal encounters variations in impedance, the resultantreflections appearing at the point of introduction may be compared inphase, time, and amplitude with the original signal. Analysis of thereflected signal may indicate the nature (i.e., resistive, inductive, orcapacitive) of the impedance variation in the transmission system and,since distance is related to time and the amplitude of the reflectedstep is directly related to impedance, the analysis may also indicatethe location thereof, being the position of the impedance change alongthe electrically conductive element.

Put another way, as electromagnetic surface waves (which may be known astransverse electromagnetic waves) propagate along an electricallyconductive element 240, signal energy may be attenuated responsive tothe electrical impedance of the environment within its influence alongits travel path. Accordingly, this reduction in signal voltage may serveas a basis for indicating changes in impedance in an area or regionsurrounding the electrically conductive element 240. For instance,electrical conductivity and volumetric water content may affect theimpedance of an area or region surrounding the electrically conductiveelement 240 and, therefore, may cause a variation in the attenuation ofsuch a signal or waveform.

Explaining further, TDR may be conceptually compared to a “lumpedcircuit load” transmission analogy. The transmission path may be assumedto comprise a lumped circuit having a load impedance at the end of thetransmission line (e.g., a coaxial cable) of known characteristicimpedance as well as the impedance of the surrounding environmentencountered by the electromagnetic surface waves traveling therealong.Thus, as the impedance of the surrounding environment changes, TDR mayindicate the nature of such changes and their relative position.Electrical impedance is related to the electrical or magnetic propertiesof material proximate to the transmission line, as well as thetransmission line itself. For example, the material dielectricpermittivity, magnetic permittivity, and the geometry of the proximatematerial, etc. may influence the electrical impedance along atransmission line; thus, these characteristics may be measured orindicated using TDR techniques.

For conceptual purposes only, a TDR technique is illustrated as it mayappear while being performed. FIG. 1D shows a graphical representationof a TDR technique. Particularly, FIG. 1D shows a graph which depictsvalues of electrical impedance as a function of length of an electricalconductor. Electrical impedance is shown on the vertical axis and isdepicted as increasing in an upward direction (i.e., from 0 to R), whilelength of the electrical conductor is shown on the horizontal axis andis depicted as increasing in a direction toward the right (i.e., from 0to L). Thus, electrical impedance is generally depicted as increasing asa function of increasing length of the electrical conductor; however, inproximity to a length L1, a distinctive change 151 in electricalimpedance may be displayed. Of course, the distinctive change 151 inelectrical impedance may be an increase or decrease, without limitation,and may proceed as a function of length as is indicated by the TDRprocess. Thus, the characteristic of a distinctive change 151 inelectrical impedance may be correlated with the length along theelectrical conductor, and the source or cause of the distinctive change151 in electrical impedance may be determined or predicted. Further, thesource or cause of the distinctive change 151 in electrical impedancemay indicate a characteristic of a barrier, in accordance with thepresent invention.

It may be appreciated that correlation between impedance changesmeasured via TDR techniques and the characteristics of the barrier maybe empirically (experimentally) or theoretically derived. Of course, anyTDR process or equipment as known in the art may be used, withoutlimitation. For instance, equipment for performing TDR analysis iscommercially available from Tektronix, Inc., of Beaverton, Oreg.

It may be appreciated that, assuming the structural elements of theinterlocking structure 230 are impervious to liquid or gas, such gas orliquid may, if the barrier filler material (not shown) is not suitableto prevent it, possibly proceed to pass through the interlockingstructure 230. For instance, FIG. 1E shows an enlarged partialcross-sectional view of an interlocking structure 230 in relation toburied waste 133. As further illustrated by path 156, liquid or gas thatpasses through interlocking structure 230, assuming that thesubstantially circular bodies 126, the female interlocking structure122, the male interlocking structure 124, and any seams therebetween,respectively, are hydraulically and pneumatically impermeable, must passthrough interlocking structure 230. Thus, as shown in FIG. 1E, liquid orgas may pass into the recess 121, about the portion of male interlockingstructure 124 disposed therein, and out of the recess 121 along path156. Accordingly, disposing protective elements 220 (shown in FIG. 1C)within the gap formed between the portion of male interlocking structure124 and the edges of substantially circular body 126 of the casingsection 120 at the mouth 137 of recess 121 may inhibit the flow of fluidor gas through interlocking structure 230.

It should be understood that, generally, one or more protective element220 may be positioned between two interlocked casing sections 120,without limitation. For instance, FIG. 1F shows an enlarged partialcross-sectional view of an interlocking structure 230, which includesone generally rectangular protective element 220 abutting and compressedagainst an edge of substantially circular body at the mouth 137 ofrecess 121. Protective element 220 also includes one electricallyconductive element 240, as described hereinabove. Alternatively, FIG. 1Gshows an enlarged partial cross-sectional view of an interlockingstructure 230 which includes one generally square protective element220, which further includes one electrically conductive element 240.Generally square protective element 220 abuts and is compressed againstan inner wall of channel feature 123 of female interlocking structure122. Disposing at least one protective element 220, the protectiveelement 220 including at least one electrically conductive element 240within the gap in an interlocking structure 230 between two casingsections 120, may, in turn, bias or position the male interlockingstructure 124 in relation to the female interlocking structure 122.

More generally, it should also be understood that one or more protectiveelements 220, according to the present invention may be positionedwithin or upon a portion of barrier 140, without limitation. Thus, whileit may be desirable to position a protective element 220 generallywithin or proximate to interlocking structures 230 of a barrier 140, thepresent invention is not so limited. For instance, at least oneprotective element 220 may be positioned between the substantiallycircular bodies 126 of adjacent casing sections 120 or upon at least onecasing section 120, without limitation.

For instance, FIG. 1H shows an enlarged partial cross-sectional view ofan interlocking structure 230 including generally square protectiveelements 220 which are disposed above and below mouth 137 of recess 121.In addition, each generally square protective element 220 may include,as shown in FIG. 1H, at least one conductive element 240. As shown inFIG. 1H, generally square protective elements 220 abut, and may becompressed between, the substantially circular bodies 126 of adjacentcasing sections 120. Accordingly, the relative position of thesubstantially circular bodies 126 of adjacent casing sections 120 may bedetermined via cooperative engagement between the male interlockingstructure 124 and the female interlocking structure 122. For instance,positioning stub 139 disposed within female interlocking structure 122may position the substantially circular body 126 including the maleinterlocking structure 124 within a desired proximity in relation to thesubstantially circular body 126 including the female interlockingstructure 122. Accordingly, disposing protective elements 220 betweenthe substantially circular bodies 126 of adjacent casing sections 120may inhibit the flow of fluid or gas through interlocking structure 230.Also, the at least one conductive element 240 disposed within each ofprotective elements 220 may be used for performing TDR. Accordingly, theat least one conductive element 240 disposed within each of protectiveelements 220 may be used for indicating at least one characteristic ofthe barrier, including interlocking structure 230.

Of course, there may be many different configurations of theinterlocking structure 230 between two casing sections 120. Forinstance, as shown in FIG. 2A, which shows a cross-sectional view of twointerlocked casing sections 120, an at least one female interlockingstructure 122 and an at least one male interlocking structure 124 may bedisposed external to the respective bores 127 of casing sections 120.Also, male interlocking structure 124 may comprise a generally T-shapedoutwardly extending feature, relative to the substantially circular body126 of casing section 120. Similar to the configuration shown in FIG.1B, interlocking structure 230 may be formed by a female interlockingstructure 122 disposed about an associated male interlocking structure124. Combinations of at least one female interlocking structure 122 andat least one male interlocking structure 124, which are either internalor external to the bore 127 of a casing section 120, are contemplated bythe present invention, without limitation.

In a further alternative, FIG. 2B shows a cross-sectional view of twointerlocked casing sections 120 similar to those shown in FIG. 1B, butincluding a male interlocking structure 124 comprising a generallyT-shaped outwardly extending feature, relative to the substantiallycircular body 126 of casing section 120. Such a configuration may bedesirable for limiting the variability in the relative positions thattwo interlocked casing sections 120 may occupy while interlocked.

Considering FIGS. 1C, 2A, and 2B in relation to FIG. 1E, it may beappreciated that placement of at least two electrically conductiveelements 240 along a predicted leakage path 156 of leachate throughinterlocking structure 230 may be desirable. For instance, placement ofa first electrically conductive element (not shown) and at least asecond electrically conductive element (not shown) along the predictedleakage path 156 at different locations therealong may facilitateindicating the progression of a leak through the interlocking structure230 of the present invention via TDR. In addition, it should also beunderstood that more than two electrically conductive elements (notshown) may be disposed along a predicted leakage path 156 for indicatingthe presence or progression of a gas or liquid leak therethrough.Further, it may also be appreciated that placement of one or moreprotective elements (not shown) along path 156 may substantially impedea leak flowing therealong.

Turning to FIG. 3A, which shows an enlarged partial cross-sectional viewof an interlocking structure 230 of the present invention, one or moreelectrically conductive elements 240 disposed generally within each ofprotective elements 220 may be employed to indicate the presence ofbarrier filler material 150 generally within interlocking structure 230.More particularly, one or more electrically conductive elements 240generally within protective elements 220 may be used to indicate thatbarrier filler material 150 has been disposed proximate thereto. Such anindication may be desirable to verify the integrity of the interlockingstructure 230.

In further detail, FIG. 3B shows a simplified schematic longitudinal(i.e., along the length of a casing section) cross-sectional view, inthe region of reference line B-B of FIG. 3A, showing protective elements220, electrically conductive elements 240 disposed therein, and maleinterlocking structure 124 of interlocking structure 230. Thecross-hatching shown in FIG. 3B indicates presence of barrier material150, and is not associated with the different materials which maycomprise male interlocking structure 124 or protective elements 220.Length, labeled “L” may include one or more casing section (FIG. 1A) oran entire casing string (FIG. 1A). Electrically conductive elements 240disposed along length “L” may be desirable for indicating acharacteristic of the environment proximate thereto, by way of TDR.

For instance, turning back to FIG. 3A, an initial TDR process may beperformed prior to disposing barrier filler material 150 within theinterlocking structure 230; thus, baseline or initial TDR data may bereceived or stored. Then, barrier filler material 150 may be disposedwithin interlocking structure 230 and afterwards, a subsequent TDRprocess may be performed. If, for instance, the barrier filler material150 is disposed so as to substantially uniformly fill the recess 121, asshown in FIG. 3A, comparison between the initial and the subsequent TDRprocess may indicate such.

On the other hand, if, for example, barrier filler material 150 isdisposed as shown in FIGS. 3C and 3D, which show a partialcross-sectional view of interlocking region 230 and a simplifiedschematic longitudinal (i.e., along the length of a casing section)cross-sectional view of interlocking structure 230, respectively, theinitial TDR data and the subsequent TDR data may be compared anddiscontinuity 166 in the barrier filler material 150 disposed within theinterlocking structure 230 may be indicated. It should be noted, forclarity, that FIG. 3D shows protective elements 220, electricallyconductive elements 240 disposed therein, and male interlockingstructure 124 of interlocking structure 230. However, the cross-hatchingshown in FIG. 3D indicates presence of barrier material 150, and is notassociated with the different materials which may comprise maleinterlocking structure 124 or protective elements 220.

Put another way, comparing initial TDR data to subsequent TDR data mayindicate regions where the barrier filler material 150 may be differentfrom other regions of barrier filler material 150. Particularly,comparing initial TDR data to subsequent TDR data may indicate theabsence of barrier filler material 150 within regions along the lengthof an interlocking structure 230, proximate to electrically conductiveelements 240.

In addition, as discussed above, TDR techniques may indicate the generalposition, labeled “x” in FIG. 3D, that discontinuity 166 occupies alongthe length “L” of the electrically conductive element 240. Accordingly,a position along the length of electrically conductive element 240 maybe correlated to a position along the length of a casing section 120, acasing string 142, or both. Thus, the relative position of discontinuity166 may be indicated via TDR.

Alternatively, TDR may be performed during the disposal of barrierfiller material 150 within interlocking structure 230. Therefore, theprogress of a flow front of barrier filler material 150 as it advancesalong the length of a casing string 142 may be monitored. For instance,if barrier filler material 150 comprises a hardenable or thickeningfluid or slurry, TDR may be performed while the barrier filler materialexhibits a flowable state (i.e., freely movable). Thus, such a processmay indicate one or more discontinuities 166 (e.g., voids, such as airpockets, or other regions of differing composition), along the length ofthe one or more electrically conductive elements 240 that barrier fillermaterial 150 does not “fill” or occupy, as discussed above. Further,upon such indication, remedial measures may be taken to ameliorate adiscontinuity 166. For instance, in the case of an unfilled “bubble” ofgas comprising discontinuity 166 that may exist in barrier fillermaterial 150 entering or passing through the interlocking structure 230,characteristics of the barrier filler material 150 may be adjusted, ifpossible, to facilitate eradication of the discontinuity 166. Forinstance, flow characteristics (i.e., flow rate, duration of flow, flowpulsing, etc.) or material properties (i.e., viscosity, temperature,etc.) of the barrier filler material 150 may be altered duringdisposition thereof within interlocking structure 230. Of course, thesame or similar procedures may be performed during filling of the bore127 of a casing string 120 or during filling of any other regionutilizing barrier filler material 150.

Also, subsequent to at least partially or substantially filling theinterlocking structure 230 with barrier filler material 150, periodicTDR processes may be performed to monitor a characteristic of theregions proximate to the one or more electrically conductive element240. For instance, the presence of water or other fluid may be indicatedby TDR processes. Furthermore, as discussed above in relation to FIG.1D, the general path of a liquid or gas from a waste sought to becontained by a barrier (FIG. 1A) through an interlocking structure 230between adjacent casing strings (FIG. 1A) forming same may be predicted,to some extent, by the geometry of the interlocking structure 230 or asotherwise known in the art. Of course, electrical time domainreflectometry may be performed via the at least one electricallyconductive element more than once, selectively, at random, on a periodicbasis or a combination thereof prior to, during, or after substantiallyfilling the interlocking structure 230 with barrier filler material 150.

In another aspect of the present invention, a protective element 220 mayinclude more than one electrically conductive element 240. FIG. 4 showsan enlarged partial cross-sectional view of an interlocking structure230 as shown in FIG. 1B. More particularly, FIG. 4 shows two protectiveelements 220, wherein each protective element 220 includes twoelectrically conductive elements 240. As shown in FIG. 4, protectiveelements 220 may be disposed between the male interlocking structure 124and the edges of substantially circular body 126 at the mouth 137 ofrecess 121. Providing more than one electrically conductive element 240at least partially within a protective element 220 may provide more thanone location for performing TDR, redundancy in measurement capability,or both, as well as the capability of developing a profile of a leakthrough barrier 140.

In another aspect of the present invention, the electrical signal orwaveform that is communicated through an electrically conductive elementof the present invention may be configured or adjusted for measurementor indication of particular characteristics. For instance, the relativesignal magnitude (voltage or amperage) may be adjusted over suitableranges in relation to the properties of an electrically conductiveelement over which it is to be communicated. Also, the time varyingnature, if any, of the signal may be configured for indication ormeasurement of particular properties, without limitation. Therefore, itwill be appreciated that one or more electrically conductive elements240 according to the present invention may be disposed within a barrier(FIG. 1A) and may be positioned, sized, and configured to indicatedifferent characteristics thereof. Alternatively, the same electricallyconductive element 240 may be used to indicate different characteristicsof the barrier (FIG. 1A) with which it is associated by communicatingdifferent waveforms therethrough for performing TDR.

Although embodiments of the present invention described hereinaboveinclude at least one electrically conductive element 240 which is atleast partially within a protective element 220, the present inventionis not so limited. Rather, an electrically conductive element 240 may beseparate from a protective element 220 of the present invention. Forinstance, an electrically conductive element 240 suitable for performingTDR may comprise a conductive wire, a coaxial cable, a shieldedconductive wire, an insulated conductive wire, or combinations thereofas known in the art. Further, more generally, an electrically conductiveelement 240 of the present invention may be disposed generally upon orwithin a barrier 140. For instance, an electrically conductive element240 may be disposed within the bore 127 of one or more casing strings142, as described hereinbelow.

For example, FIG. 5A shows a partial cross-sectional view of twoadjacent casing strings which form a portion of barrier 140 according tothe present invention disposed within formation 108. Interlockingstructure 230, as shown in FIG. 5A, is substantially identical to theinterlocking structure 230 shown in FIG. 1C. More specifically,interlocking structure 230 may comprise protective elements 220 that maybe disposed along both sides of the male interlocking structure 124 andthe mouth 137 of recess 121. Further, according to the presentinvention, protective elements 220 may each include one or moreelectrically conductive elements 240 that may extend therein along thelength of a casing string. As mentioned above, each of electricallyconductive elements 240 may comprise a coaxial cable or anotherelectrical conductor which is electrically capable of carrying anelectrical signal suitable for performing electrical time domainreflectometry.

In addition, a plurality of electrically conductive elements 240 may bedisposed proximate to the casing sections 120 of the casing strings (notshown) of the barrier 140. For instance, FIG. 5A shows at least one ofthe plurality of electrically conductive elements 240 may be positionedwithin a bore 127 of a casing section 120, within a recesses 121 of acasing section 120, or proximate the exterior of the substantiallycircular body 126 of a casing section 120, without limitation. Such aconfiguration may be suitable for monitoring of barrier filler material150 disposed within at least one of a bore 127 of a casing section 120,a recess 121 thereof, and an interlocking structure 230 thereof, withoutlimitation. Alternatively, such a configuration may provide formonitoring of leakage through barrier 140. Monitoring of the integrityof barrier filler material 150 or leakage through barrier 140 may beperformed via TDR, as explained hereinabove.

Of course, referring to FIGS. 1A-5A, one or more electrically conductiveelements 240 may be disposed within or upon a casing section 120 priorto its disposal within the formation 108. However, it may be desirableto protect against damage to an electrically conductive element 240 ifdisposing an electrically conductive element 240 within or upon a casingsection 120 prior to disposal within the formation 108. Thus, thepresent invention contemplates that an electrically conductive element240 may be protected by a portion of the casing section 120, such as,for instance, a protective stand-off, or an indentation or channelformed in the casing section 120.

In further detail, FIG. 5B shows that an electrically conductive element240 may be placed generally within an indentation or channel 252 formedin the substantially circular body 126 of a casing section (not shown).Of course, indentation or channel 252 may be arcuate, rectangular, ortapered (i.e., dove-tail) in shape, without limitation. Further, anelectrically conductive element 240 may be placed within recess 121proximate at least one stand-off 254, wherein the at least one stand-off254 is sized and positioned to protect the electrically conductiveelement 240 proximate thereto from damage due to relative movementbetween the male interlocking structure 124 and the female interlockingstructure 122. Such a configuration may be desirable for protection ofthe electrically conductive elements 240. Alternatively, an indentation252 or at least one stand-off 254 may be sized and positioned to providea space or envelope along the length of a casing string 142 fordisposition of an electrically conductive element 240 therein subsequentto formation of a barrier (not shown).

While the present invention has been described herein with respect tocertain preferred embodiments, those of ordinary skill in the art willrecognize and appreciate that it is not so limited. Rather, manyadditions, deletions and modifications to the preferred embodiments maybe made without departing from the scope of the invention as hereinafterclaimed. In addition, features from one embodiment may be combined withfeatures of another embodiment while still being encompassed within thescope of the invention as contemplated by the inventors. Therefore, theinvention is to encompass all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the following appended claims.

1. A method of indicating at least one characteristic of at least aportion of a containment system providing a barrier adjacent a selectedregion of a subterranean formation, the method comprising: forming abarrier by providing a plurality of casing strings, wherein each of theplurality of casing strings is laterally adjoined to at least one otheradjacent casing string of the plurality of casing strings by way of aninterlocking structure; disposing at least one electrically conductiveelement along at least a portion of a length of at least one of theplurality of casing strings forming the barrier; substantially fillingat least one interlocking structure extending between two laterallyadjacent casing strings of the plurality with barrier filler materialperforming a first electrical time domain reflectometry using the atleast one electrically conductive element to determine at least onecharacteristic associated with the barrier prior to substantiallyfilling the at least one interlocking structure with the barrier fillermaterial; and performing at least a second electrical time domainreflectometry process subsequent to substantially filling the at leastone interlocking structure with the barrier filler material.
 2. Themethod of claim 1, wherein disposing the at least one electricallyconductive element along the at least a portion of the length of the atleast one of the plurality of casing strings forming the baitercomprises disposing at least one electrically conductive elementproximate the interlocking structure extending laterally between twocasing strings of the plurality.
 3. The method of claim 1, furthercomprising performing electrical time domain reflectometry a pluralityof times.
 4. The method of claim 3, wherein performing electrical timedomain reflectometry the plurality of times comprises performingelectrical time domain reflectometry substantially continuously.
 5. Themethod of claim 3, wherein performing electrical time domainreflectometry the plurality of times comprises performing electricaltime domain reflectometry at predetermined intervals, randomly, or both.6. The method of claim 1, wherein performing time domain reflectometryto determine the at least one characteristic associated with the barriercomprises detecting a change in impedance of the at least oneelectrically conductive element.
 7. The method of claim 6, furthercomprising determining a location of the change in impedance along theat least one electrically conductive element.
 8. The method of claim 1,further comprising comparing results of the first electrical time domainreflectometry process to results of the at least a second electricaltime domain reflectometry process.
 9. A method of indicating at leastone characteristic of at least a portion of a containment systemproviding a barrier adjacent a selected region of a subterraneanformation, the method comprising: forming a barrier by providing aplurality of casing strings, wherein each of the plurality of casingstrings is laterally adjoined to at least one other adjacent casingstring of the plurality of casing strings by way of an interlockingstructure; disposing at least one electrically conductive element alongat least a portion of a length of at least one of the plurality ofcasing strings forming the barrier; substantially filling at least oneinterlocking structure extending between two laterally adjacent casingstrings of the plurality with barrier filler material; and performingelectrical time domain reflectometry using the at least one electricallyconductive element to determine at least one characteristic associatedwith the barrier during the substantially filling the at least oneinterlocking structure with the barrier filler material.
 10. A method ofindicating at least one characteristic of at least a portion of acontainment system providing a barrier adjacent a selected region of asubterranean formation, the method comprising: forming a barrier byproviding a plurality of casing strings, wherein each of the pluralityof casing strings is laterally adjoined to at least one other adjacentcasing string of the plurality of casing strings by way of aninterlocking structure; disposing at least one electrically conductiveelement along at least a portion of a length of at least one of theplurality of casing strings forming the barrier; substantially fillingat least one interlocking structure extending between two laterallyadjacent casing strings of the plurality with barrier filler material;performing electrical time domain reflectometry using the at least oneelectrically conductive element to determine at least one characteristicassociated with the barrier wherein determining the at least onecharacteristic associated with the barrier comprises determining apresence of a discontinuity in the barrier filler material responsive toperforming electrical time domain reflectometry.
 11. The method of claim10, further comprising indicating a location of the discontinuity alonga length of the at least one electrically conductive element responsiveto performing electrical time domain reflectometry.
 12. The method ofclaim 1, wherein determining the at least one characteristic associatedwith the barrier by performing electrical time domain reflectometrycomprises indicating leakage of a material through the barrier.
 13. Themethod of claim 12, wherein indicating leakage of the material throughthe barrier further comprises performing time domain reflectometry via aplurality of electrically conductive elements, wherein each of theplurality of electrically conductive elements is positioned generallyalong an anticipated leakage path through the barrier.
 14. The method ofclaim 1, further comprising disposing the at least one electricallyconductive element at least partially within an elongated protectiveelement located proximate the interlocking structure.
 15. The method ofclaim 14, further comprising disposing the elongated protective elementin a gap between portions of the interlocking structure.